Module Specification
Module is the way to improve the
structure design by break down the problem for solving it into independent
task.
Advantages of Module –
I.
It breakdown the problem into independent modules so
the complexity of the problem can be minimized.
II.
Each independent module can be easily assigned to the
various members of the development team.
III.
Module can be easily run and tested independently from
another.
Top-Down design approach:-
It is a technique of breakdown a
problem into major tasks to be performed. Each task is then further broken down
into separate sub task and so on until each sub task is sufficiently simple to
be written as a self contained module.
In
Top-Down design we initially describes the problem at the highest level that descript
what must be done and It does not show how it must be done. Top-Down methods
are used throughout the system analysis and design process. The value of using
top-down approach, starting at general level and to understand and gain the
system and moving down to the levels of greater details.
Advantages of Top-Down Approach –
I.
By dividing of the problem into number of sub problems
we have made it easier to share problem development.
II.
It is easy to debug a large program as a number of
smaller units rather than one big problem.
III.
It is good way to delay decision on problems whose
solution is not readily prepared.
IV.
It allows a programmer to remain on top of a problem
and view the developing solutions. The solution always proceeds from the
highest level to the lowest level.
V.
It becomes an ideal structure for managing the
implementation of a computer program using team of programmers.
Bottom-Up design approach:-
When we face a large and complex
problem , it is difficult to see how the whole thing can be done so it may
easier to solve the part of the problem individual, taking the common and easy
aspects first and then more difficult task and finally gather them all together
to form complete solution, this is called bottom-up approach.
The
bottom-up approach suffers from disadvantage that the part of the program may not
fit together very easily and there may be a lack of consistency between modules
and reprogramming have to be done.
Module Cohesion & Coupling:-
i.)
Modules:
Module
is represented by a rectangle box with module name. After defining general
purpose of each program it is divided into modules. Each of which performs a
single function.
For
Ex:-
An accounting system consists of
many separate modules that are invoked one at a time as user wish to perform
particular function. Each upper level module leads to using one or more lower
level modules until the desired function is performed.
ii.)
Connectors:
Connections
between modules are represented using links, modules. It is drown by on arrow
line in downward direction.
iii.)
Coupling:
It
refers to the strength of relationship between modules in the system. Coupling
measures the degree to which two distinct modules are bound together.
It
can be of two types –
a)
Data
Coupling:
It
carries data between two modules and it can have upward or downward direction.
Data flows are shown using named arrow with a small circle at one end. It is
shown by an arrow with blank circle at the tail.
b)
Control
Coupling:
It
carries info about data couple and does not carry any data. It is shown by an
arrow with filled circle at the tail.
iv.)
Cohesion:
It
is used to denote the intra module strength. It is a relationship among
elements within a module. A system designer should aim at minimizing coupling
and maximizing cohesion to get modular design. Designer insures that each
module performs a specific function and can be developed independently. A good
design has low coupling i.e. low interdependence between modules and high
cohesion i.e. high interrelationship within the elements of a single module.
Using Top-Down approach to plan the
software for a system is no guarantee that errors will be avoided totally so
properly modularized, cohesive system, the contents of the module are designed
such that they perform a specific function and easily understood by people.
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